Proceedings of 2009 ASME Joint Rail Conference 

JRC2009 

March 3-5, 2009 Pueblo, Colorado, USA 

JRC2009-63060 

MECHANICAL PROPERTIES OF TANK CAR STEELS RETIRED FROM THE FLEET 

Peter C. McKeighan 

Exponent – Failure Analysis Associates 

Wood Dale, Illinois, USA 

David Y. Jeong 

Volpe National Transportation Systems Center 

US Department of Transportation 

Cambridge, Massachusetts, USA 

Joseph W. Cardinal 

Southwest Research Institute 

San Antonio, Texas, USA 

ABSTRACT 

As a consequence of recent accidents involving the release 

of hazardous materials (hazmat), the structural integrity and 

crashworthiness of railroad tank cars have come under scrutiny. 

Particular attention has been given to the older portion of the 

fleet that was built prior to steel normalization requirements 

instituted in 1989. 

This paper describes a laboratory testing program to 

examine the mechanical properties of steel samples obtained 

from tank cars that were retired from the fleet. The test 

program consisted of two parts: (1) material characterization 

comprised of chemical, tensile and Charpy V-notch (CVN) 

impact energy and (2) high-rate fracture toughness testing. 

In total, steel samples from 34 tank cars were received and 

tested. These 34 tank cars yielded 61 different pre-1989 

TC128-B conditions (40 shell and 21 head samples), three tank 

cars yielded seven different post-1989 TC128-B conditions 

(four shell and three head samples), and six tank cars yielded 

other material (A212, A515, and A285 steel) conditions (six 

shell and five head samples). 

The vast majority of the TC128-B samples extracted from 

retired tank cars met current TC128-B material specifications. 

Elemental composition requirements were satisfied in 97 

percent of the population whereas the required tensile 

properties were satisfied in 82 percent of the population. 

Interpretation of the high-rate fracture toughness tests required 

dividing the pre-1989 fleet into quartiles that depended on year 

of manufacture or age, and testing three tank cars per quartile. 

Considering the high-rate fracture toughness results at 0oF for 

the pre-1989 fleet, 100 percent of the oldest two quartiles, 58 

percent of the second youngest quartile, and 83 percent of the 

youngest quartile exhibited adequate or better fracture 

toughness (defined as toughness greater than 50 ksi√in). Highrate fracture toughness at –50oF was adequate for 83 percent of 

two quartiles (the youngest and second oldest), but the other 

two quartiles exhibited lower toughness with only 33 (2nd

youngest) to 50 percent (oldest) exhibiting adequate properties. 

INTRODUCTION 

The safe transport of hazardous materials (hazmat) by 

railroad tank cars is a concern to Government regulatory 

agencies and industry stakeholders. Both Government and 

industry have sponsored research over the past several decades 

to maintain the structural integrity of railroad tank cars under a 

broad range of loading conditions that vary from the normal 

operating environment to rare events such as accidents. 

In the late 1980s, the Association of American Railroads 

recommended practices were changed to require all subsequent 

pressure cars to be fabricated from normalized TC128-B steel. 

Prior to 1989, non-normalized steel was predominantly used. 

Non-normalized steel has a higher transition temperature and 

potentially lower fracture toughness when compared to 

normalized steel. 

However, the structural integrity of railroad tank cars 

during accidents has recently come under greater scrutiny due 

to three particular accidents involving the release of hazmat: 

(1) a derailment that occurred near Minot, North Dakota on 

January 19, 2002 [1], (2) a train collision that occurred in 

Macdona, Texas on June 28, 2004 [2], and (3) a train collision 

that occurred in Graniteville, South Carolina on January 6, 

2005 [3]. Each of these accidents resulted in a release of 

hazmat and subsequent fatalities. Based on findings from 

investigations of these accidents, the National Transportation 

Safety Board (NTSB) made a series of safety recommendations 

to the Federal Railroad Administration (FRA). In particular, 

the following recommendation was issued following the Minot 

accident, and reiterated following the Macdona accident: 

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1 
“Conduct a comprehensive analysis to determine the 

impact resistance of the steels in the shells of pressure cars 

constructed before 1989. At a minimum, the safety analysis 

should include results from dynamic fracture toughness tests 

and/or the results of nondestructive testing techniques that 

provide information on material ductility and fracture 

toughness. The data should come from a statistically 

representative sampling of the shells of the pre-1989 pressure 

tank car fleet.” 

In its role to provide technical support to the FRA, the 

Volpe National Transportation Systems Center (Volpe Center) 

enlisted experimental expertise to carry out a laboratory testing 

program to address the NTSB recommendation. This paper 

briefly summarizes the major results from this testing program. 

The laboratory testing program was focused on quantifying 

overall material performance. In particular, it determined the 

basic material characterization (analysis of chemical or 

elemental composition, tensile properties and Charpy v-notch 

impact energy) parameters as well as the high-rate fracture 

toughness at rates consistent with what might be experienced 

during accidents such as derailments and train collisions. 

Material for the testing program was obtained from tank 

cars that were retired from the fleet. A more comprehensive 

and detailed description of the entire testing program can be 

found in the final technical report [4] that is currently available 

on the Volpe website (http://www.volpe.dot.gov/sdd/pubstank.html). 

PRESSURE TANK CAR FLEET CHARACTERIZATION 

Data were obtained from the Universal Machine Language 

Equipment Register (UMLER), which is maintained by the 

Association of American Railroads, in order to examine the 

make-up of the pressure tank car fleet in terms of material 

distribution and age. The data shown in Figure 1 represent a 

snapshot of the fleet at the time when the laboratory test 

program was initiated (April 2005). Over 93 percent of the 

fleet is fabricated from TC128-B with four percent made from 

A212-B. The remaining three percent of the pressure tank car 

fleet is fabricated from other materials, which include A515, 

A516 and A285-C as the most numerous choices in this small 

percentage of the fleet. 

An overlay of two plots is indicated in Figure 2 providing 

a sense of the material obtained and the fleet make-up. The 

bottom plot shows the cumulative number of pressure cars as a 

function of year of manufacture for (a) the whole fleet 

(represented by the triangles) and (b) the pre-1989 fleet 

(represented by the squares). Approximately 75 percent of the 

pressure car fleet was built prior to 1998. Moreover, onequarter of the fleet was produced before 1976 and one-half 

before 1990. The top plot shows the makeup of the cars from 

which the material for the test program was obtained. Material 

from these retired cars were donated from owners and 

operators of the pressure car fleet. 

MATERIAL CHARACTERIZATION 

Basic material characterization was conducted in 

accordance with standard test methods that are developed and 

published by the American Society for Testing and Materials 

(ASTM), as listed in Table 1. Although all materials (Figure 1) 

were examined, the focus of the results presented herein will be 

on TC128-B material, the most prevalent material found in the 

pressure car fleet. 

Table 1: Standard Material Characterization Tests 

Type of Characterization ASTM Standard 

Chemical (elemental) analysis ASTM E415 [5] 

Tensile properties ASTM A370 [6] 

CVN impact energy ASTM A23 [7] 

Chemical Composition

In the chemical analysis, sixteen elements were measured and 

reported, even though the TC128-B composition specification 

calls for controlling only nine distinct elements. In summary, 

59 of 61 TC128-B samples (97 percent) met composition 

requirements. One of the deviations was due to a slightly 

higher carbon content than allowable (0.32 wt % as opposed to 

the criteria of <0.29 wt %). The second deviation was due to 

higher (0.05 wt %) than allowable (< 0.04 wt %) sulfur content. 

No other disparities with regard to chemical content were noted 

during testing. However a cautionary point should be noted; 

the applicability of modern AAR material specification to 

vintage material (some of it 30 years old) is not clear. 

UMLER: April 2005 data

Material Used in Tank Car Fabrication

TC128-B

A212-B

A516-Gr70A515-Gr70

A285-C

Other

TC128-A

Percentage of pre-1989 Pressure Tank Car Fleet

0

1

2

3

4

5

60

70

80

90

100 93.3%

4.3%

0.8% 0.5% 0.4% 0.4% 0.3%

Figure 1: Steel Types in Pre-1989 Pressure Tank Car Fleet 

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2 
UMLER: April 2005 data

Year of Manufacture

19561958196019621964196619681970197219741976197819801982198419861988199019921994199619982000200220042006

% of Pressure Car Fleet Produced Before

0

10

20

30

40

50

60

70

80

90

100

whole fleet

pre-1989 fleet only

1960's 1970's

1980's

1990's

2000's

1950's 1956 1958 1960

19621964196619681970197219741976197819801982198419861988199019921994199619982000200220042006

No. of Candidate 

Tank Cars/Material

0

1

2

3

4 TC128-B 

A212-B/G 

A515-Gr70 

A285-C 

Figure 2: Cumulative Distribution of Pressure Tank Car Fleet and Tank Cars Used for Testing 

Tensile Properties

Measurements of tensile properties included: yield 

strength, ultimate strength, and ductility in terms of percent 

elongation and percent reduction in area. The customary gage 

length specimen utilized was a 2-inch gage length, although 

material limitations sometimes required testing subsize (1-inch 

or 1.4-inch) gage length specimens. All specimens were 

oriented transverse to the primary plate axis for the shell 

specimens although in the case of the head specimens the 

orientation was arbitrary. 

Table 2: Tensile Property Specifications for TC128-B 

Property Allowable* 

Ultimate Tensile Strength 81 to 101 ksi 

Yield Strength Greater than 50 ksi 

Elongation Greater than 22% 

*AAR Manual of Standards and Recommended Practices and 

Specifications for Tank Cars, M-1002, Appendix M. 

Charpy Impact Energies

Charpy tests were conducted at three different 

temperatures: ±50oF and 0oF. CVN specimens from the shell 

material were oriented with the primary axis of the specimen in 

the transverse plate direction and the crack direction orthogonal 

and in the plane of the plate. 

Tensile and Impact Property Summary

A summary of the average tensile properties and CVN 

impact data is shown in Table 3. The data trend as a function 

of time, with the tank car fleet divided up into quartiles, is 

depicted in Figures 3-5. A total of 61 TC128-B conditions 

were examined: 40 shell and 21 head conditions. 

In summary, two material conditions exhibited slightly 

lower than allowable yield strength (45 and 48 ksi versus the 

minimum 50 ksi). Three material conditions exhibited 

ductilities slightly lower (in the range of 19-21%) than allowed 

(percent elongation in excess of 22%). The allowable UTS 

range (81-101 ksi) was exceeded in nine samples (two with 

higher and seven with lower values). In only one case was the 

measured strength level in excess of 5 ksi lower than the 

allowable (approximately 7 ksi low). Given requirements on 

ductility, ultimate and yield strengths, all except eleven tank car 

material conditions (82% of the total) were within the required 

TC128-B specifications. 

There is no current applicable TC128-B CVN energy level 

required. As noted in Table 3 and Figure 5, considerable scatter 

was evident in the highest temperature CVN value. The lowest 

observed impact energies were in the shell at the lowest -50۫° F 

test condition where single digit energies were observed. 

Contrast this with the highest energies observed for the 

normalized material (head or post 1989) where energies in 

excess of 25 ft-lbs were commonly observed. 

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3 
Table 3: Statistical analysis (averages and standard deviations) of TC128-B material characterization testing. 

Subset A: 1969 and before build date, 25% of the pre-1989 pressure car fleet 

Subset B: 1970 to 1976 build date, 25-52% (27% total) of the pre-1989 pressure car fleet 

Subset C: 1977 to 1979 build date, 52-72% (20% total) of the pre-1989 pressure car fleet 

Subset D: 1980 and later build date, 28% of the pre-1989 pressure car fleet 

Data Tank # Cars UTS, ksi YS, ksi Elong, percent RA, percent CVN at +50°F CVN at 0°F CVN at -50°F 

Set Posn (conds) N avg 2SD N avg 2SD N avg 2SD N avg 2SD N avg 2SD N avg 2SD N avg 2SD

all H&S 25 (61) 122 88.8 13.45 122 61.1 13.33 122 26.3 7.15 122 54.3 14.78 110 31.9 49.07 141 19.9 33.60 110 9.8 17.58

S-only 25 (40) 80 89.3 14.72 80 60.5 15.31 80 24.8 5.90 80 50.2 9.81 74 21.0 18.77 96 12.5 13.55 74 6.3 9.18 

H-only 19 (21) 42 87.7 10.45 42 62.3 8.01 42 29.2 5.52 42 62.1 8.69 36 54.4 60.69 45 35.5 41.43 36 16.9 21.83

A H&S 11 (28) 56 87.6 12.56 56 60.0 10.87 56 26.6 6.93 56 55.1 14.56 52 32.7 40.94 59 19.6 31.84 52 9.2 14.52

S-only 11(16) 32 87.6 13.75 32 58.9 13.49 32 24.9 5.95 32 50.0 9.66 30 20.9 13.93 34 12.6 13.93 30 5.7 7.94 

H-only 11 (12) 24 87.6 11.06 24 61.6 4.50 24 28.9 5.37 24 62.0 5.69 22 48.8 43.82 25 29.1 39.06 22 14.0 15.98

B H&S 7 (17) 34 90.0 13.37 34 60.8 15.39 34 26.0 7.39 34 52.8 12.07 26 23.1 21.56 47 17.4 26.92 26 6.9 8.76 

S-only 7 (13) 26 90.9 13.58 26 59.9 16.34 26 24.6 6.00 26 50.3 6.67 22 20.1 14.16 37 11.1 9.08 22 5.5 3.94 

H-only 3 (4) 8 87.0 11.37 8 63.5 10.89 8 30.3 3.96 8 60.9 11.68 4 39.3 28.58 10 40.7 17.51 4 15.0 10.95

C H&S 4 (8) 16 89.7 11.98 16 62.9 12.40 16 25.3 5.78 16 53.4 13.14 16 33.4 67.27 19 18.5 21.00 16 12.6 23.45

S-only 4 (6) 12 89.4 13.88 12 62.5 14.01 12 24.8 5.49 12 51.6 11.96 12 22.8 27.72 15 16.9 18.71 12 10.3 14.77

H-only 2 (2) 4 90.8 1.87 4 64.2 6.23 4 26.8 6.45 4 58.7 11.73 4 65.0 112.68 4 24.5 27.74 4 19.5 40.08

D H&S 3 (8) 16 89.4 17.43 16 63.8 16.16 16 26.9 8.63 16 55.3 21.27 16 42.6 73.86 16 29.6 58.10 16 13.6 26.36

S-only 3 (5) 10 90.7 20.55 10 64.8 17.48 10 24.7 6.80 10 48.8 14.28 10 21.3 28.27 10 10.8 13.28 10 5.6 8.94 

H-only 3 (3) 6 87.2 10.72 6 62.2 14.60 6 30.7 5.61 6 66.3 8.12 6 78.0 72.67 6 61.0 47.28 6 27.0 23.66

normalized 3 (7) 13 81.7 5.71 13 55.4 5.14 13 31.2 7.47 13 62.0 16.62 12 77.3 94.95 15 52.2 63.22 12 26.4 38.33

# Cars = No. of unique tank cars, conds = unique material conditions, H = head, S = shell, avg = average, 2SD = 2 std. deviations Strength, ksi

40

60

80

100

120

ultimate

yield

average ±2 standard deviations shown

Full Pre-1989 

TC128-B 

Population

25 tankcars

60 matl. conds.

Subset A

1965-1969, 

11 cars,

25% of 

pre-89 fleet

Subset B

1970-1976, 

7 cars,

27% of 

pre-89 fleet

H & S

shell-only

head-only

1989 and

more recent

TC128-B

3 cars

Subset C

1977-1979, 

4 cars,

21% of 

pre-89 fleet

Subset D

1979-1988, 

3 cars,

28% of 

pre-89 fleet

Figure 3: Strength properties of the tank car fleet. 

Percent

0

20

40

60

80

100

elongation

reduction of area

average ±2 standard deviations shown

Full Pre-1989 

TC128-B 

Population

25 tankcars

60 matl. conds.

Subset A

1965-1969, 

11 cars,

25% of 

pre-89 fleet

Subset B

1970-1976, 

7 cars,

27% of 

pre-89 fleet

H & S

shell-only

head-only

1989 and

more recent

TC128-B

3 cars

Subset C

1977-1979, 

4 cars,

21% of 

pre-89 fleet

Subset D

1979-1988, 

3 cars,

28% of 

pre-89 fleet

Figure 4: Ductility properties of the tank car fleet. 

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CVN energy, ft-lbs

0

20

40

60

80

100

120

140

160

180

200

+50°F

0°F

-50°F

average ±2 standard deviations shown

Full Pre-1989 

TC128-B 

Population

25 tankcars

60 matl. conds.

Subset A

1965-1969, 

11 cars,

25% of 

pre-89 fleet

Subset B

1970-1976, 

7 cars,

27% of 

pre-89 fleet

Subset C

1977-1979, 

4 cars,

21% of 

pre-89 fleet

H & S

shell-only

head-only

Subset D

1979-1988, 

3 cars,

28% of 

pre-89 fleet

1989 and

more recent

TC128-B

3 cars

Figure 5: CVN impact energy of the tank car fleet. 

Tensile/Impact Property Correlation with Composition

It is useful to examine if any correlations exist between 

key compositional quantities and the tensile/impact 

performance. One theory tested is a correlation between sulfur 

content and upper shelf impact energy [8]. This correlation, 

shown in Figure 6, clearly indicates no functional relationship 

between sulfur content and upper shelf CVN energy. This plot 

does provide an excellent indication of the low CVN energies 

associated with the shell material compared with the effectively 

normalized head material. However the highest energies and 

cleanest compositions are observed in the most recent, 

normalized (post-1989) condition although data are few. 

Finally, the correlation between carbon content and yield 

strength is shown in Figure 7. As before with sulfur content, 

there does not appear to be any clear functional relationship 

between carbon and strength. Although in some cases the error 

bars are fairly broad, the amount of data is likely sufficient to 

conclude no functional link between these variables. 

Source:

No. of cars:

No. of samples:

Primary variables:

Sulfur, weight percent

0.005 0.010 0.015 0.020 0.025 0.030 0.035 0.040

CVN energy at 50°F, ft-lbs

0

25

50

75

100

125

150

175

pre-1989 (shell)

pre-1989 (head)

post-1989 (shell)

post-1989 (head)

±1 standard deviation shown

tank car fleet

25

58

shell and head

Figure 6: Poor correlation between impact energy and 

tensile properties for TC128-B steel. 

TC128-B

Carbon Content, weight percent

0.16 0.18 0.20 0.22 0.24 0.26 0.28 0.30 0.32 0.3

Yield Strength, ksi 30

40

50

60

70

80

±2 standard deviations shown

Figure 7: Poor correlation between carbon content and 

yield strength for TC128-B steel. 

HIGH-RATE FRACTURE TOUGHNESS TESTING 

Tests were conducted in accordance with ASTM E399 [9] 

and ASTM E 1820-01 [10] at two different temperatures: 0 oF 

and –50oF. Compact tension specimens with a width of 2-inch 

were utilized for testing. The thickness of the specimens 

depended upon the starting thickness of the shell/head product; 

the majority of specimens were 0.5-0.6 inch thick. These 

specimens were oriented in the T-L direction and configured 

with an eddy current displacement gage that provided sufficient 

responsiveness for the high rate testing. In addition, a 

displacement gage was also utilized on the front face of the 

specimens and strain gages on the back face of the specimens. 

Redundant load measurements were available with 

instrumented grips and a conventional, high response load cell. 

A slack adapter was utilized in the loading train to insure that 

the fastest strain rate was applied to the specimens. 

During high rate toughness testing, the integrity of the 

load-displacement behavior is often less than optimum (due 

primarily to dynamic effects). When this occurs, it is often 

difficult to apply a conventional offset analysis procedure to 

determine a KIc from the test data. Therefore, during this 

testing the reported toughness is a Kmax toughness 

corresponding to the maximum applied stress intensity factor 

calculated using the initial crack length and the maximum load 

(assuming no crack advance or tearing). This approach yields 

conservative values where higher levels of plasticity are 

observed (non-brittle conditions) and also minimizes bias in the 

test results. To account for plasticity, a correction to the Kmax

value was applied to yield a KJmax value so as to accommodate 

the plasticity under the load-displacement curve consistent with 

methods presented in the ASTM elastic-plastic toughness test 

procedures. 

A framework for interpreting fracture toughness values 

was developed previously by Anderson and McKeighan [11] 

based upon existing design codes for pressure vessels, bridges 

and other structure. Classifications for different values of 

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5 
fracture toughness obtained from the Kmax approach were 

defined as follows: 

Spec ID No.:

Nominal Temp:

Crack Opening Displacement, mils

0 5 10 15 20 25

Load, kips

0

1

2

3

4

5

Back Face Strain, microstrain

0 -1000 -2000 -3000 -4000 -5000

load line displ.

back face strain

79a-SB-2

-50° F • Less than 50 ksi√in Poor toughness 

• 50 – 100 ksi√in Adequate toughness 

• 100 – 200 ksi√in Good toughness 

• Greater than 200 ksi√in Excellent toughness 

Typical Behavior and Overall Toughness Results

Example fracture surfaces that indicate the type of 

fractures observed are shown in Figure 8. The gross fracture 

morphology was rough and typically indicative of high energy 

fracture. Some texture was noted especially in the older 

product where lamellar layers, consistent with grain structure, 

were sometimes observed on the fracture surface. 

Fracture toughness was measured at loading or strain rates 

that might be experienced during accidents such as derailments 

and collisions. An estimate of the strain rate during an accident 

was made based on collision dynamics analysis. Assuming that 

an impact speed of 40 miles per hour creates a dent depth of 20 

inches, the corresponding strain rate is 35 inch per inch per 

second. The observed actuator rates were typically on the order 

of 50-65 inch/second. This rate translated into a strain rate, on 

the back face of the specimen, of 2-4 in/in/second. In terms of 

applied stress intensity factor, the high rate toughness tests 

were on the order of 50,000-100,000 ksi√in/second. 

Figure 9: Typical “brittle” behavior (1000 mils = 1 inch). 

Spec ID No.:

Nominal Temp:

Crack Opening Displacement, mils

0 20 40 60 80 10

Load, kips

0

0

1

2

3

4

5

6

7

8

9

10

11

Back Face Strain, microstrain

0 -2500 -5000 -7500 -10000 -12500 -15000

load line displ.

back face strain

74b-SA-3

0° F

Some material behaved in a classic, linear-elastic mode 

such as that shown in Figure 9. The initial load-displacement 

behavior is highly linear until peak load occurs when the 

specimen fails. This is contrasted to the more ductile behavior 

noted in Figure 10 where higher levels of nonlinearity are 

evident in the initial slope and upon reaching peak load 

extensive plasticity (or crack advance) is apparent. Tests that 

exhibit extensive ductility like this are apparent with a KJmax

toughness value that is nearly identical to the Kmax value. This 

is contrasted to the case of ductile behavior where KJmax

toughness is much greater than Kmax toughness. 

 (a) Pre-1989 TC128-B material Figure 10: Typical “ductile” behavior (1000 mils = 1 inch). 

 

 A statistical summary of the fracture toughness test 

data is shown in Table 4 with toughness measure as a function 

of the different subsets of the fleet population prior to 1989. In 

addition, data is also provided for normalized TC128-B (post1989) as well as a summary of the behavior noted with older 

A212-B material. The number of datapoints, range, average 

and standard deviation of the Kmax or KJmax measure is indicated 

for all data, shell-only and head-only material.

(b) Post-1989 TC128-B material 

Figure 8: Typical fracture surfaces observed. 

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Table 4: Statistical analysis (averages and standard deviations) of TC128-B and A212-B fracture toughness. 

Subset A: 1969 and before build date, 25% of the pre-1989 pressure car fleet 

Subset B: 1970 to 1976 build date, 25-52% (27% total) of the pre-1989 pressure car fleet 

Subset C: 1977 to 1979 build date, 52-72% (20% total) of the pre-1989 pressure car fleet 

Subset D: 1980 and later build date, 28% of the pre-1989 pressure car fleet 

Kmax or KJmax fracture toughness, ksi√in (for different materials or subsets of a given material) 

Test Tank TC128-B Subset A TC128-B Subset B TC128-B Subset C TC128-B Subset D TC128-B Normalized A212-B 

Temp Posn N avg SD N Avg SD N avg SD N avg SD N avg SD N avg SD

0°F H&S 12 116 37 14 122 39 13 78 35 12 109 52 10 107 23 6 68 41

71 S-only 8 126 40 10 116 38 9 77 37 8 83 29 7 96 12 3 51 5 

H-only 4 96 21 4 137 44 4 80 36 4 162 50 3 134 21 3 86 57

-50°F H&S 6 76 46 6 77 49 6 52 19 6 62 23 5 60 10 4 45 10

S-only 4 86 55 4 56 15 4 47 17 4 48 11 4 58 9 2 41 1 

H-only 2 55 10 2 119 76 2 60 27 2 90 3 1 71 n/a 2 50 15

 H = head, S = shell, avg = average, 2SD = 2 std. deviations Kmax or KJmax toughness, ksi√in

0

50

100

150

200

250

all

shell-only

head-only

TC128-B

Subset A

TC128-B

Subset B

TC128-B

Subset C

TC128-B

Subset D

TC128-B

normalized

A212-B

0° F Tests

Occurrences

0

5

10

15

0° F Tests

error bars ±1 standard deviation

 

Kmax or KJmax toughness, ksi√in

0

50

100

150

200

250

all

shell-only

head-only

TC128-B

Subset A

TC128-B

Subset B

TC128-B

Subset C

TC128-B

Subset D

TC128-B

normalized

A212-B

-50° F Tests

Occurrences

0

5

10

15

-50° F Tests

error bars ±1 standard deviation

(a) (b) 

Figure 11: Graphical summary of measured fracture toughness at (a) 0°F and (b) -50°F. 

The data in Table 4 are plotted in Figure 11. There is no 

question that for TC128-B material subset A and B (the oldest 

50% of the fleet), the global average behavior at 0°F is of a 

higher magnitude toughness than observed in the youngest 

50% of the fleet. This is counter-intuitive and suggests that the 

newer vintage fleet is not as tough as the older vintage fleet. 

Nevertheless, the broad standard deviations clearly suggest that 

the toughness variability is too high to conclude that this is a 

statistically significant finding. 

The data in Figure 11(a) at 0°F also shows that the poorest 

performing material is the A212-B. Average toughness values 

are lower than observed in any of the other materials and the 

lower bound levels also the lowest when taking into account 

variability. Clearly any type of TC128-B outperforms the 

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7 
A212-B material. The wide variability and low average also 

suggests that a large percentage of the A212-B fleet will exhibit 

“poor” toughness levels. 

One advantage with the post-1989 normalized TC128-B is 

that the apparent variability in toughness appears less than with 

the older vintage TC128-B. Although the average toughness 

observed with the newer vintage, normalized material is not 

significantly different from the pre-1989 fleet (the averages are 

actually less than observed in the older 50% of the fleet), the 

smaller standard deviation band means that the lower bound 

toughness when subtracting 2 standard deviations still is in 

excess of 50 ksi√in. This suggests that the post-1989 

normalized material outperforms all other materials or 

conditions in Figure 11(a). 

Material performance in Figure 11(b) for -50°F is 

generally poor with low average values. The sample size is 

small too, and this presumably influences the standard 

deviation bands indicated. A similar trend is observed as with 

the 0°F data though, with higher average toughness for the 

oldest half of the fleet when compared to the younger half. On 

balance, the best behaving material at -50°F is the post-1989, 

normalized TC128-B. However it is clear that if the error bar 

were extended to ±2 standard deviations, the range would dip 

below 50 ksi√in and into the poor toughness regime. 

Toughness Correlations

The word ‘toughness’ is used for two separate quantities: 

impact toughness and fracture toughness. Impact toughness is 

an energy measurement (e.g., Joules or ft-lb) which is 

commonly obtained from the CVN test. Fracture toughness is a 

calculated value for the critical stress intensity factor (in units 

of MPa√m or ksi√in) based on standard fracture mechanics 

tests. Relationships between these quantities are empirical. 

The correlation between high-rate fracture toughness and 

CVN energy at a temperature of 0oF is shown in Figure 12. 

The error bars represent variability in the measurements in 

terms of one standard deviation above and below the mean 

value. Also shown in Figure 12 is the Roberts-Newton 

equation [12], which was developed for lower shelf or 

transition behavior. Similarly, Figure 13 shows the correlation 

for results at –50oF. Except for a few outliers, the test data lie 

above the Roberts-Newton equation. Moreover, the RobertsNewton equation appears to provide a reasonable lower-bound 

estimate of fracture toughness for non-normalized TC128-B 

tank car steel. 

DISCUSSION 

The high rate fracture toughness testing performed herein 

has generated structural results, not material property results in 

the strictest sense of ASTM “valid” properties. Reasons for the 

invalid test results were insufficient thickness and occasionally 

non-linear load displacement behavior. Therefore there is some 

structural dependence of these results and the data would 

therefore be expected to exhibit size effects. A clear indication 

of the structural nature of the test results can be obtained by 

examining the limit ratio defined as the percent of limit load 

(calculated as per ASTM E813 using flow stress) for the 

specimen at the maximum applied load (see Figure 14). A 

value of 0.8 would imply that at the maximum load, the 

specimen sustained 80% of the limit load possible with that 

specimen/material combination. Conversely a value of 1.25 

would imply that the load was at 125% of limit load. Had the 

specimens been larger, the limit load ratio would have been 

less. However, these specimens were about as large as possible 

without significantly thinning the specimen and not testing full 

wall thickness (e.g. they would have been too curved to test). 

Also shown on Figure 14 is a line illustrating the limit ratio 

of 0.67, which can be arguably used to represent the limit of 

applicability for K-based linear-elastic fracture mechanics 

(LEFM). For the specimens whose limit ratio was underneath 

(less or below) this line, LEFM would apply. For the tests 

above the line, plasticity conditions dominated and an elasticplastic parameter governed toughness (such as the KJmax

parameter utilized herein). KIc is clearly an unsuitable test 

method or toughness quantifier for this non-LEFM regime. 

0oF

CVN Energy (ft-lb)

0 25 50 75 100 125

High-Rate Fracture Toughness (ksi√in)

0

50

100

150

200

Head Tests

Shell Tests

Roberts-Newton

Kc=9.35(CVN)0.63

Error bars represent ±1 standard deviation

Figure 12: Toughness trend with TC128-B energy at 0oF. 

-50oF

CVN Energy (ft-lb)

0 25 50 75 100 125

High-Rate Fracture Toughness (ksi√in)

0

50

100

150

200

Head Tests

Shell Tests

Roberts-Newton

Kc=9.35(CVN)0.63

Error bars represent ±1 standard deviation

Figure 13: Toughness trend with TC128-B energy at –50oF. 

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8 
Test Sample Identification

66b-SA66a-SA

66a-HA

68b-SA68b-SB

68b-HA

74b-SA

74b-HA

75a-SA

75a-HA

76b-SF

76b-SA

77a-SD

78b-SA

78b-HA

79a-SA79a-SB

79a-HA

80a-SA

80a-HA

81a-SB82a-SA82a-SB

82a-HA

94a-SA94a-SB

94a-HA

94b-SA

94b-HA

65a-SA

65a-HA

66c-SA

66c-HA

Limit Load Ratio in Fracture Specimen 0.25

0.50

0.75

1.00

1.25

1.50

1.75 TC128-B

Normalized

TC128-B A212-B

subset A subset B subset C subset D

Figure 14: Limit load ratio observed in fracture tests. 

It is likely that plane-strain dominance was observed in the 

test specimen involved in this program. The first clear 

indication of this is the extent of flat fracture (without shear 

lips) observed in the specimen and documented in Figure 8. 

Although the specimens are flat, at high applied K-levels a 

significant amount of through-thickness “necking” is observed. 

Nevertheless, the most recent version of E399 has relaxed the 

thickness requirement. In fact, there currently is no thickness 

requirement, but a remaining ligament size requirement of 

2.5(KIc/σYS)

2 is still present in the standard. 

These structurally significant fracture toughness data, 

though not material properties, are still useful when assessing 

the damage tolerance of rail tank cars. Kushner [13] provides 

an extensive discussion in a recent NTSB document related to 

the significance of dynamic fracture toughness to the tank car 

integrity program. He makes several excellent points regarding 

the significance of toughness. Since the NTSB 

recommendations that led to this work, there has been a 

considerable amount of work trying to better understand what 

occurs in a tank car accident (for instance, the recent Next 

Generation Rail Tank Car Program co-sponsored by Dow 

Chemical Company, Union Pacific Railroad and Union Tank 

Car Company). We have the benefit today of making use of 

this and other recently derived expertise when examining the 

structural integrity issues. 

Controlling the material strength and fracture toughness 

alone are likely not sufficient for preventing all failures in 

current tank car designs. Understanding the material 

parameters that control puncture is an active area of research 

for the tank car industry. It is likely that static strength and 

fracture toughness play an important role in controlling 

whether rupture and puncture occur, although how the two 

contribute to the failure behavior is as yet not fully understood. 

For the more typical accident, shell and head puncture are 

the critical occurrences that must be avoided. Despite what 

others have publically stated, an individual with extensive 

failure analysis experience was given access to the Minot 

wreckage and the observation was made that most if not all of 

the fractures observed on the different tank cars involved in the 

incident also had some form of puncture in or adjacent to them. 

This individual’s belief was that the first step in the failure 

process was likely puncture and the second step, given 

sufficient energy, was separation of the tank. Given this 

scenario, the critical property, and the parameter most critical 

for design, is not the fracture toughness of the material but 

rather the puncture resistance. 

Unfortunately we do not have a firm and definitive 

understanding yet of what material properties contribute to 

enhanced puncture resistance. Some of this work is currently 

underway, and initial findings appear somewhat promising in 

terms of better understanding what parameters drive puncture. 

Properties such as a materials fracture toughness and static 

strength likely play some type of role, however the significance 

of these parameters in dictating puncture performance is not yet 

clear or well-understood. 

CONCLUDING REMARKS 

The testing program described in this paper yielded the 

following major conclusions: 

1) No clear trend was observed between chemical, tensile, or 

CVN impact energy properties and tank car build date. In 

total, 61 different pre-1989 TC128-B conditions were 

examined. Eighteen other conditions were examined 

including non-TC128-B material as well as post-1989 

normalized TC128-B. 

2) The vast majority of the TC128-B samples extracted from 

retired tank cars met current TC128-B material 

specifications. 

3) Fifty-nine of sixty-one samples satisfied the chemistry 

requirements for TC128-B. In one case, the two anomalies 

included high carbon content, and in the other case, high 

sulfur content. 

4) Eighty-two percent of the tank car samples met tensile 

property requirements for TC128-B. Two TC128-B 

conditions exhibited slightly lower yield strengths than 

allowed. Three tank car conditions exhibited slightly 

lower ductility than allowed. Nine tank car conditions 

violated the required range of ultimate strength (two 

exceeded and seven were less). 

5) The pre-1989 tank car fleet was subdivided into four 

groups, or quartiles, depending on age. High-rate, lowtemperature fracture toughness testing was performed on 

samples from each quartile. Criteria developed by 

Anderson and McKeighan [11] were used to quantify 

toughness performance. Considering the oldest quartile, 

100 percent of the 0oF and 50 percent of the –50oF tests 

exhibited adequate or better toughness. Considering the 

second oldest quartile, 100 percent of the 0oF and 83 

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9 
This material is declared a work of the U.S. Government and is not subject to copyright protection in the United States. Approved for public release; distribution is unlimited. 

10 

percent of the –50oF tests exhibited adequate or better 

toughness. Considering the second youngest quartile, 58 

percent of the 0oF and 33 percent of the –50oF tests 

exhibited adequate or better toughness. Considering the 

youngest quartile, 83 percent of the 0oF and 83 percent of 

the –50oF tests exhibited adequate or better toughness. 

6) Testing was also performed on newer TC128-B material as 

well as A212-B material. Considering the post-1989 

vintage, normalized TC128-B material, 100 percent of the 

0oF and 80 percent of the –50oF tests exhibited adequate or 

better toughness. Considering the A212-B material, 67 

percent of the 0oF and 25 percent of the –50oF tests 

exhibited adequate or better toughness. 

7) The extent of scatter observed in the fracture toughness 

testing was quite large, which prevents making definitive 

conclusions regarding toughness variations with age. 

ACKNOWLEDGEMENTS 

The work described in this paper was sponsored by FRA 

Office of Research and Development. Dr. Thomas Raslear is 

the Acting Chief of the Equipment and Operating Practices 

Division. Mr. Francisco Gonzalez is the FRA program 

manager for research on railroad tank cars. 

The testing program was conducted under a Volpe Center 

task order contract with Foster-Miller, Inc. (FMI) while the 

principal author was employed by Southwest Research Institute 

(SwRI). SwRI was a subcontractor to FMI in this task order 

contract. The authors gratefully acknowledge Ms. Loretta 

Mesa at SwRI for her help in preparing the final technical 

report for this extensive test program. 

The Association of American Railroads Tank Car 

Committee is acknowledged for their assistance in procuring 

material for this effort. In particular, the following 

organizations are graciously recognized for providing material 

to this effort: American Railcar Industries, Canadian Pacific 

Railway, CSX Corporation, Federal Railroad Administration, 

GATX Corporation, Kansas City Southern Railway, Occidental 

Chemical, Transport Canada, Union Pacific Corporation and 

Union Tank Car Company. 

REFERENCES 

[1] National Transportation Safety Board, “Derailment of 

Canadian Pacific Railway Freight Train 292-16 and 

Subsequent Release of Anhydrous Ammonia Near Minot, 

North Dakota January 18, 2002,” Railroad Accident 

Report NTSB/RAR-04/01, March 2004. 

[2] National Transportation Safety Board, “Collision of 

Union Pacific Railroad Train MHOTU-23 With BNSF 

Railway Company Train MEAP-TUL-126-D With 

Subsequent Derailment and Hazardous Materials Release, 

Macdona, Texas, June 28, 2004,” Railroad Accident 

Report NTSB/RAR-06/03, July 2006. 

[3] National Transportation Safety Board, “Collision of 

Norfolk Southern Freight Train 192 With Standing 

Norfolk Southern Local Train P22 With Subsequent 

Hazardous Materials Release at Graniteville, South 

Carolina January 6, 2005,” Railroad Accident Report 

NTSB/RAR-05/04, November 2005. 

[4] McKeighan, P.C., “Mechanical Properties of Tank Car 

Steels Retired from the Fleet,” Southwest Research 

Institute Report to Volpe Center, August 2008. 

[5] ASTM Standard E415, 2005, “Standard Test Method for 

Optical Emission Vacuum Spectrometric Analysis of 

Carbon and Low-Alloy Steel,” ASTM International, West 

Conshohocken, PA, www.astm.org. 

[6] ASTM Standard A370-05, “Standard Test Methods and 

Definitions for Mechanical Testing of Steel Products,” 

ASTM International, West Conshohocken, PA, 

www.astm.org. 

[7] ASTM Standard A23-05, “Standard Test Methods for 

Notched Bar Impact Testing of Metallic Materials,” 

ASTM International, West Conshohocken, PA, 

www.astm.org. 

[8] Anderson, T. L. and Kirkpatrick, S. W., “Quantifying and 

Enhancing Puncture Resistance in Railroad Tank Cars 

Carrying Hazardous Materials - Phase I: Preliminary 

Study,” Final Report for the Chlorine Institute, Structural 

Reliability Technology, Inc. and Applied Research 

Associates, Inc., August 2006. 

[9] ASTM Standard E399-06, “Standard Test Method for 

Linear-Elastic Plane-Strain Fracture Toughness KIC of 

Metallic Materials,” ASTM International, West 

Conshohocken, PA, www.astm.org. 

[10] ASTM Standard E1820-01, “Standard Test Method for 

Measurement of Fracture Toughness,” ASTM 

International, West Conshohocken, PA, www.astm.org. 

[11] Anderson, T.L., McKeighan, P.C., “Interpreting Fracture 

Toughness Magnitudes of Tank Car Steels: Relating Kbased Toughness Range with Material Adequacy,” August 

2005. 

[12] Roberts, R., Newton, C. “Interpretive Report on SmallScale Test Correlations with KIC Data,” Welding Research 

Council Bulletin 265, 1981, pp. 1-18. 

[13] Kushner, A.S., “NTSB Assessment of the Significance of 

Fracture Toughness on Tank Car Safety in Railroad 

Accidents,” Technical Memorandum, February 23, 2007.